The present invention relates to a liquid crystal display (LCD) devices and methods of fabrication therefor, more particularly, to in-plane switching (IPS) LCD devices and methods of fabrication therefor.
In general, in-plane switching (IPS) mode LCDs have pixel electrodes and common electrodes which apply electric fields to a liquid crystal layer parallel to the substrate on which the electrodes are formed, as described, for example, in European Patent Application No. 93307154.0 (Publication No. 0 588 568 A2). As shown in FIG. 1, a gate line 1 is formed in a transverse direction and a data line 11 is formed in a longitudinal direction. A common electrode line 2 having a T-shaped extension with sections 3, 4 is formed parallel to the gate line 1, and may be formed from the same material as the gate line 1. A longitudinal section 3 extends to the gate line 1 and a transverse section 4 connected to one end of the longitudinal section 3 extends parallel to the adjacent gate line 1. A thin film transistor TFT is formed near the intersection of the gate line 1 and the data line 11, and has a gate electrode which is a portion of the gate line 1, a source electrode which is a portion of the data line 11, and a drain electrode 12 which may be made of the same material as the data line 11 and extends from a pixel electrode 16. The pixel electrode 16 is rectangular in shape, and includes two sides parallel to the data line 11 and two sides perpendicular to the data line 11 which overlap the common electrode line 2 and its transverse section 4. The longitudinal section 3 of the common electrode line 2 passes over the center of the rectangle defined by the pixel electrode 16. In an alternative arrangement illustrated in FIG. 2, a drain electrode 12 of a thin-film transistor TFI is connected to an H-shaped pixel electrode 16 having a longitudinal section 13 parallel to the data line 11 and two transverse sections 14 extending perpendicular to the data line 11, while the common electrode line 2 has a looplike portion extending therefrom.
In each of these electrode arrangements, electric fields may be generated between the extensions of the common electrode line 2 and the pixel electrode 16, causing rotation of the optical axes of liquid crystal molecules between the electrodes 2, 16 toward the direction of electric fields. Light passes through the liquid crystal layer with a transmittance T which may be determined by a conventionally-used formula:
T=sin22xcex8xc2x7sin2xcfx80xc2x7(xcex94nxc2x7d)/xcex
where xcex8 is the angle between the long axes of the liquid crystal molecules and the direction of polarization, An is refractive anisotropy of the liquid crystal material, xcex is wavelength of the light, and d is the gap, also known as xe2x80x9ccell gapxe2x80x9d, between the two substrates of the device. Based on this formula, Japanese Patent Application No. 7-225388 has stated that it is preferable for xcex94nxc3x97d to be set between 0.21-0.36 xcexcm in cases where xcex8=45xc2x0 in order to achieve optimal transmittance. Unfortunately, however, the gap between substrates for this range of the product of refractive anisotropy and cell gap typically is small for conventionally-used liquid crystal materials. Consequently, a display device fabricated to achieve this product of refractive anisotropy and cell gap may be difficult and expensive to produce.
In light of the foregoing, it is an object of the present invention to provide in-plane switching type liquid crystal displays which may be efficiently produced.
It is another object of the present invention to provide in-plane switching type liquid crystal display devices which have optimal transmittance with increased cell gap in comparison to conventional devices.
This and other objects, features and advantages are provided according to the present invention by liquid crystal display devices for which the product (xcex94nxc3x97d) of the refractive anisotropy (xcex94n) of the liquid crystal material in the display and the cell gap (d) between the panels confining the liquid crystal material is between 0.36 xcexcm and 0.45 xcexcm, preferably when the angle (xcex8) between the alignment direction of alignment surfaces of the panels and the polarization direction of light passing through the liquid crystal material contained by the alignment surfaces is around 45xc2x0. The present invention arises from the experimental discovery that desirable transmission characteristics may be achieved at higher values of the product of refractive anisotropy and cell gap than conventionally predicted. Accordingly, devices may be fabricated with a larger cell gap, allowing the use of less expensive fabrication techniques.
In particular, according to the present invention, an in-plane switching type liquid crystal display device includes opposed first and second panels, defining a gap therebetween, the first and second panels including first and second electrodes, spaced laterally apart in the gap. A quantity of a liquid crystal material is disposed in the gap between the first and second panels, wherein a product of a refractive anisotropy of the liquid crystal material and the gap between the first and second panels is in a range between 0.36 xcexcm and 0.45 xcexcm. Preferably, the gap between the first and second panels is in a range between 4 xcexcm and 5 xcexcm, and the refractive anisotropy is in a range between 0.067 and 1.1016. Each of panels preferably has an alignment surface which is operative to align molecules of the liquid crystal material along an alignment direction, and a polarizer, attached to one of the first and second panels, selectively permits light having a polarization of 45xc2x0 with respect to the alignment direction to pass through the quantity of liquid crystal material.
According to method aspects, an in-plane switching type liquid crystal display device is fabricated by forming opposed first and second panels, defining a gap therebetween, the first and second panels including first and second electrodes, spaced laterally apart in the gap. A quantity of a liquid crystal material is then placed in the gap between the first and second panels, wherein a product of a refractive anisotropy of the liquid crystal material and the gap between the first and second panels is in a range between 0.36 xcexcm and 0.45 xcexcm. Improved liquid crystal display devices are thereby provided.